How to Use Regex Function in Terraform: Syntax and Examples

In Terraform, the regex() function checks if a string matches a regular expression pattern and returns the matching substring. Use regex("pattern", string) to extract the first match or regexall("pattern", string) to get all matches as a list.

Syntax

The regex() function takes two arguments: a regular expression pattern and the string to search. It returns the first substring that matches the pattern. If no match is found, it causes an error. The regexall() function returns a list of all matching substrings or an empty list if none match.

• pattern: The regular expression to match.
• string: The text to search within.

terraform

regex(pattern, string)
regexall(pattern, string)

Example

This example shows how to extract the first number from a string using regex() and all numbers using regexall(). It demonstrates pattern matching and outputting results.

terraform

variable "input_string" {
  default = "User123 has 456 points and 789 credits"
}

output "first_number" {
  value = regex("\\d+", var.input_string)
}

output "all_numbers" {
  value = regexall("\\d+", var.input_string)
}

Output

first_number = "123"
all_numbers = ["123", "456", "789"]

Common Pitfalls

Common mistakes include:

• Using regex() when no match exists, which causes an error.
• Not escaping special characters in the pattern properly.
• Confusing regex() (returns first match) with regexall() (returns all matches).

Always test your regex patterns and handle cases where matches might not exist.

terraform

/* Wrong: regex() with no match causes error */
output "no_match_error" {
  value = regex("abc", "def")
}

/* Right: use regexall() to safely get matches or empty list */
output "safe_no_match" {
  value = regexall("abc", "def")
}

Output

safe_no_match = []

Quick Reference

Function	Description	Return Type	Behavior if No Match
regex(pattern, string)	Returns first substring matching pattern	string	Error if no match
regexall(pattern, string)	Returns list of all matching substrings	list(string)	Empty list if no match

Key Takeaways

Use regex(pattern, string) to get the first match substring in Terraform.

Use regexall(pattern, string) to get all matches as a list safely.

regex() errors if no match is found; regexall() returns an empty list instead.

Escape special characters in regex patterns properly with double backslashes.

Test regex patterns to avoid runtime errors in Terraform configurations.